1. Field of the Invention
The present invention relates to an optical coupling arrangement and, more particularly, to an optically isolated coupling arrangement.
2. Description of the Prior Art
Optical couplers are perhaps one of the most ubiquitous of all passive optical components and may be found in virtually any optical communication system. One use of optical couplers which is the subject of much current study is in the field of fiber amplifiers, since these amplifiers require that both a communication signal and a pump signal be coupled into the amplifying medium, with the medium itself coupled to the optical signal path. The successful operation of fiber amplifiers may be dependent upon the ability to couple maximum pump power into the amplifying gain medium, as well as the ability to control the multiple reflections present within the system. As reported in an article entitled "An 11 Gbit/s, 151 km Transmission Experiment Employing a 1480 nm Pumped Erbium-Doped In-Line Fiber Amplifier" by M. Z. Iqbal et al. appearing in IEEE Photonics Technology Letters, Vol. 1, No. 10, October 1989 at pp. 334-6, the performance of systems utilizing erbium-doped fiber amplifiers is found to be degraded by the presence of signal-spontaneous beat noise and reflection-induced lasing within the amplifying medium. Iqbal et al. propose a system for multi-gigabit applications which utilizes a pair of isolators, with a first isolator located at the transmitter output and a second isolator located at the amplifier input. Although such isolators may improve the system performance, the size and complexity of the resultant system is also increased.
A single isolator approach is discussed in an article entitled "Impact of Multiple Reflection Noise in Gbit/s Lightwave Systems with Optical Fibre Amplifiers" by J. L. Gimlett et a. appearing in Electronic Letters, Vol. 25, No. 20, September 1989, at pp. 1394-4. Gimlett et al. propose an arrangement including a counter-propagating pumped fiber amplifier, with an optical isolator located at the amplifier input. A dichroic coupler is utilized to provide the pump signal to the fiber amplifier. As with the Iqbal et al. arrangement described above, the optical isolator and pump coupler of Gimlett et al. are separate, physically displaced devices.
A need, remains in the art, therefore, for providing an isolated coupled arrangement for applications such as fiber amplifiers.